1. Field of the Invention
The present invention relates to protection components including four alternate semiconductor layers, such as thyristors, gateless thyristors, and both mono and bidirectional Shockley diodes.
2. Discussion of the Related Art
Various circuits using such protection components and improvements of such components are described in the patents and patent applications U.S. Pat. No. 5,274,524, U.S. Pat. No. 5,243,488, EP-A-490,788, U.S. Pat. No. 5,272,363, EP-A-542,648, EP-A-561,721, and FR92/14,793 (B1712, B1713, B1731, B1810, B1841, B1958, B2072).
Various improvements have been made to such components to improve their protection function, that is, to increase the accuracy of their breakover threshold and/or to render the breakover threshold programmable, and to improve the reliability of the components. These protection components are increasingly used because of their switching-on characteristics (the voltage across their terminals drops to a very low value during the occurrence of an overvoltage), because of their subsequent small size, and because of their fast switching ability. These protection components are used in particular in the protection of telephone lines.
In a known way, one can use a one-way Shockley diode with a rectifying circuit, or a bidirectional Shockley diode mounted between two wires of a telephone line. One can use delta-connected or star-connected Shockley diodes, wherein a first terminal is connected to a first wire of the telephone line, a second terminal is connected to a second wire of the telephone line, and a third terminal is connected to a reference voltage, usually ground.
However, since the protection components must remain within tolerable size limits, these components are intended to withstand a predetermined maximum energy surge. Beyond this maximum energy surge, the protection component is at risk of being destroyed. The protection components are designed so that this destruction corresponds to a short-circuiting of the protection component. In fact, if destruction corresponded to an open circuiting of the component, the circuit to be protected could be destroyed.